This invention relates to a composite article and method of producing composite articles as semiconductor devices, such as photovoltaic cells. More particularly, this invention relates to providing a composite article having improved efficiency.
Composite articles, which are used as semiconductor devices such as for photovoltaic cells, comprise a metal layer, such as stainless steel, having a semiconductor material coated thereon to provide a thin surface layer. Conventional semiconductor material suitable for the purpose are amorphous silicon, gallium arsenide, cadmium sulfide and indium sulfide.
With composite articles of this type wherein an alloy such as stainless steel is used as the substrate, the surface to be coated is typically characterized by surface irregularities. These irregularities or imperfections on the surface are caused by phenomenon such as grain boundary etching during pickling, roll marks transferred from the workrolls used during cold rolling and foreign material that may be embedded in the metal surface during rolling or other operations.
It has been found that these surface irregularities in constructing a semiconductor device by coating on said surfaces a conventional semiconductor material can cause poor performance in applications such as photovoltaic cells and the like, particularly from the standpoint of "shorting" in the film surface that reduces conversion efficiency or renders the cell inoperable.
In semiconductor devices, such as photovoltaic cells, for example, raised or projecting surface irregularities of the metal substrate may not be coated by the semiconductor material and may extend through a coating of semiconductor material. Though such irregularities are extremely small, they can cause localized "shorting" or other electrical discontinuities when the irregularities extend through additional layers of intermediate insulative material and semiconductor materials. Such localized "shorting" results in overall losses in conversion efficiency, and in severe cases may result in inoperable devices. Similarly, "shorting" can be caused by substrate surface irregularities which are impressions, pockets or recesses which may result in discontinuities and/or undesired contact of the semiconductor layer. Generally, any contact between two or more semiconductor material layers can result in a "shorting" of the electrical circuit of the composite article semiconductor device.
It is, accordingly, a primary object of the present invention to provide a composite article for semiconductor applications wherein the layer of semiconductor material is deposited over a smooth surface to thereby improve the performance of the composite article in semiconductor applications.